Search Results (65)

TiVCr-based alloys are well-explored body-centered cubic (BCC) materials for hydrogen storage applications that can potentially store higher amounts of hydrogen at moderate temperatures. The challenge remains in optimizing the alloy-hydrogen stability, and several transition elements have been found to support the reduction in the hydride stability. In this study, Ni and Nb transition elements were incorporated into the TiVCr alloy system to thoroughly understand their influence on the (de)hydrogenation kinetics and thermodynamic properties. Three different compositions, (TiVCr)₉₅Ni₅, (TiVCr)₉₀ Ni₁₀, and (TiVCr)₉₅Ni₅Nb₅, were prepared via arc melting. The as-prepared samples showed the formation of a dual-phase BCC solid solution and secondary phase precipitates. The samples were characterized using hydrogen sorption studies. Among the studied compositions, (TiVCr)₉₀Ni₁₀ exhibited the highest hydrogen absorption capacity of 3 wt%, whereas both (TiVCr)₉₅Ni₅ and (TiVCr)₉₀Ni₅Nb₅ absorbed up to 2.5 wt% hydrogen. The kinetics of (de)hydrogenation were modeled using the JMAK and 3D Jander diffusion models. The kinetics results showed that the presence of Ni improved hydrogen adsorption at the interface level, whereas Nb substitution enhanced diffusion and hydrogen release at room temperature. Thus, the addition of Ni and Nb to Ti-V-Cr-based high-entropy alloys significantly improved the hydrogen absorption and desorption properties at room temperature for gas-phase hydrogen storage. Full article

The effects of silicon (Si) doping on the microstructure, mechanical properties, and electrochemical corrosion behavior of dual-phase eutectic high-entropy alloys (AlCrFeNi)_100-xSi_x (x = 2, 4, 6 at.%) were systematically investigated. The results reveal that with increasing Si content, all three alloys maintain a sunflower-like eutectic microstructure composed of A2 and B2 phases, characterized by an expanding central region and a densification and refinement of the lamellar two-phase structure in the petal regions; the volume of phase B2 gradually increases, accompanied by the precipitation of nanoscale B2 particles. The test results of mechanical properties show that Si doping enhances the compressive strength and Vickers hardness but significantly reduces ductility, exhibiting a typical inverse strength–ductility relationship. Electrochemical corrosion tests demonstrate that higher Si content deteriorates corrosion resistance, with corrosion predominantly occurring in the B2 phase. Among the studied alloys, the Si₂ variant exhibits the most balanced overall performance. This work provides valuable insights into the role of Si in tuning the microstructure and properties of eutectic high-entropy alloys and methodology for their compositional design and engineering applications. Full article

Fabricating eutectic high-entropy alloys (EHEAs) via selective laser melting (SLM) presents significant potential for advanced structural applications. This study explores the microstructural evolution of Fe₃₂Cr₃₃Ni₂₉Al₃Ti₃ EHEAs fabricated by SLM under varying laser powers. Electron backscatter diffraction (EBSD) analysis revealed that samples fabricated at 200 W exhibited approximately 70% face-centered-cubic (FCC) and 30% body-centered-cubic (BCC) phases. In comparison, those processed at 160 W showed an increased FCC fraction of 85% with a corresponding reduction in BCC content. Grain size measurements indicated that BCC grains were consistently finer than their FCC counterparts. Thermal simulations demonstrated that higher laser power produced deeper melt pools and broader temperature gradients. By correlating thermal history with phase diagram data, the spatial variation in BCC content was attributed to the differential residence time in the 1350–1100 °C range. This study represents one of the first attempts to quantitatively link local thermal histories with the evolution of dual-phase (FCC + BCC) microstructures in EHEAs during SLM. The findings contribute to the improved understanding and control of phase formation in complex alloy systems, providing valuable guidance for tailoring SLM parameters to optimize the phase composition and microstructure of EHEAs. Full article

This work studies the fabrication of CoCrFeNiMo high-entropy alloy (HEA) coatings via coaxial powder-fed laser cladding, addressing porosity and impurity issues in conventional methods. The HEA coatings exhibited eutectic/hypereutectic microstructures under all laser power conditions. A systematic investigation of laser power effects (1750–2500 W) reveals that 2250 W optimizes microstructure and performance, yielding a dual-phase structure with FCC matrix and dispersed σ phases (Fe-Cr/Mo-rich). The coating achieves exceptional hardness (738.3 HV_0.2, 3.8× substrate), ultralow wear rate (4.55 × 10⁻⁵ mm³/N·m), and minimized corrosion current (2.31 × 10⁻⁴ A/cm²) in 3.5 wt.% NaCl. The friction mechanism of the CoCrFeNiMo HEA coating is that in high-speed friction and wear, the oxide film is formed on the surface of the coating, and then the rupture of the oxide film leads to adhesive wear and abrasive wear. The corrosion mechanism is the galvanic corrosion caused by the potential difference between the FCC phase and the σ phase. Full article

To expand the fundamental understanding of eutectic high-entropy alloys (EHEAs), three novel alloy systems—Cr_1.3Ni₂TiAl, CoCr_1.5NiTi_1.5Al_0.2, and V_0.3CoCr_1.2NiTi_1.1Al_0.2—were rationally designed through synergistic phase diagram analysis and thermodynamic parameter calculations. Comprehensive microstructural characterization coupled with mechanical property evaluation revealed that these alloys possess FCC+BCC dual-phase architectures with atypical irregular eutectic morphologies. Notably, progressive microstructural evolution was observed, including amplified grain boundary density and the emergence of brittle nanoscale precipitates. Mechanical testing demonstrated superior compressive yield strengths in these alloys compared to conventional FCC+BCC EHEAs with ordered eutectic structures, albeit accompanied by reduced fracture strain. The Cr_1.3Ni₂TiAl alloy exhibited optimal ductility, with a maximum fracture strain of 15.6%, while V_0.3CoCr_1.2NiTi_1.1Al_0.2 achieved peak strength, with a compressive yield strength of 1389.5 MPa. Multiscale analysis suggests that the enhanced mechanical performance arises from the synergistic interplay between irregular eutectic configurations, expanded grain boundary area, and precipitation strengthening mechanisms. Full article

Controlling multiple phases by adjusting elemental ratios and applying heat treatments effectively balances the strength and ductility of refractory high-entropy alloys. In this study, five types of V-Ti-Cr-Nb-Mo alloys were designed by varying the contents of V, Ti, and Nb, followed by annealing at 1200 °C for 8 h. The alloys’ crystal structures, microstructure evolution, and mechanical properties were systematically investigated. The V-Ti-Cr-Nb-Mo alloys exhibited a typical dendritic structure with a dual-phase (BCC + HCP) matrix. When the Nb content was maintained at 35 at.% with increasing V content, the volume fraction of the HCP phase increased, and the C14 Laves phase emerged. The as-cast alloy V₁₅Ti₃₀Cr₅Nb₃₅Mo₁₅, with a triple-phase (BCC + HCP + Laves) structure, exhibited excellent mechanical properties, including a compressive strength of 1775 MPa and a ductility of 18.2%. After annealing, the HCP phase coarsened and partially dissolved, the Laves phase precipitation reduced, and while the hardness and strength decreased, the ductility improved significantly. The annealed alloy V₅Ti₃₅Cr₅Nb₄₀Mo₁₅, with a dual-phase (BCC + HCP) structure, achieved a ductility of 26.9% under a compressive strength of 1530 MPa. This work demonstrates that multi-phase refractory high-entropy alloys can significantly enhance the strength–ductility synergy, providing an experimental foundation for the compositional design and performance optimization of refractory high-entropy alloys. Full article

Recrystallization is a critical process for tailoring the microstructure to enhance the mechanical properties of alloys. In duplex-phase alloys, the recrystallization is different due to the influence of the second phase. Hypo-eutectic high-entropy alloys (HEAs) with two phases are promising structural materials. Understanding the laws of microstructure and mechanical properties during recrystallization is essential for fabrication and application. Here, we systematically investigate the influence of recrystallization time on the microstructure and mechanical properties of an as-cast hypo-eutectic high-entropy alloy (HEA), Al₁₃Ni₃₆Cr₁₀Fe₄₀Mo₁. As the recrystallization time increases from 10 min to 8 h at 1100 °C, the cold-rolled alloy gradually completed the recrystallization process with a residual large B2 phase and equiaxed FCC grains decorated with B2 precipitation. The average grain size of the FCC phase increases slightly from 2.60 μm to 3.62 μm, while the fine B2 phase precipitates along the FCC phase’s grain boundaries. This optimized microstructure significantly improves the alloy’s tensile strength from 422 MPa to 877 MPa, while maintaining a substantial plasticity of 41%, achieving an excellent strength–ductility balance. These findings provide useful information for regulating the industrial thermomechanical treatment of dual-phase hypo-eutectic high-entropy alloys. Full article

High-entropy alloys (HEAs) possess multi-element composition and uniform structure, exhibiting superior microstructure and properties compared to traditional alloys. However, the multi-element composition of HEAs results in a complex internal composition configuration with exceptionally high hardness and strength, leading to various machining defects under cutting loading such as poor surface roughness, excessive machining temperature, and cutting tool wear. This study investigates the milling performance of FeCoNiCrMn_x HEAs with different elemental ratios subjected to various ultrasonic-assisted milling techniques, aiming to identify the better ultrasonic assisted technique and machining process parameters. The ultrasonic-assisted milling techniques include single-axis ultrasonic, dual-axis ultrasonic, and triple-axis ultrasonic. The side milling experiments were performed on three different elemental ratios of HEAs, e.g., FeCoNiCrMn_0.1, FeCoNiCrMn_0.5, and FeCoNiCrMn_1.0 workpieces. The study is divided into two phases. Each alloy workpiece undergoes side-milling experiments using two designated combinations of feed rate and radial cutting depth subjected to various ultrasonic-assisted milling techniques in the first phase. The purpose is to identify which ultrasonic-assisted milling technique may provide the better surface quality for different elemental ratios and to analyze the performance of various cutting condition combinations in terms of surface roughness and cutting tool wear. Based on the results of the first phase, the better ultrasonic-assisted milling technique is selected and an L₉ Taguchi orthogonal array is then employed for process parameter planning, by varying spindle speed, feed rate, and radial cutting depth to investigate the effects of different process parameter combinations on machining performance of HEAs with different elemental ratios. The results show that ultrasonic assistance significantly improves the cutting performance in aspects such as reduction of cutting force and cutting tool wear, and the surface quality of alloys with high Mn content. In the first phase experiment, as compared to milling without assistance, the surface roughness may be reduced up to approximately 17.86% by single-axis ultrasonic-assisted milling using the Set 1 process parameters for different elemental ratios, while it achieves up to approximately 34.4% in surface roughness and approximately 17.68% in cutting tool wear using the Set 2 process parameters. The results from the second phase of experiments reveal a more moderate fluctuation of surface roughness and an approximate reduction from 22.03% to 314.27%, with an approximate reduction from 3.64% to 54.45% in cutting force, and an approximate reduction from 0.58% to 94.77% in cutting tool wear for the higher Mn content alloy in contrast to the lower Mn content one. The integrity of the surface morphology is significantly improved as the elemental ratio, x, is increased to 1.0, resulting in a reduction in machined surface deformation and more consistent milling marks on the machined surface, which indicates a higher stable state of machining quality. Full article

This paper investigates the effect of strain rate on the mechanical deformation and microstructural development of dual-phase AlCrFe₂Ni₂ high-entropy alloy during quasi-static and dynamic compression processes. It is revealed that the as-cast AlCrFe₂Ni₂ alloy is composed of a mixture of FCC, disordered BCC, and ordered B2 crystal structure phases. The alloy shows excellent compressive properties under quasi-static and dynamic deformation. The yield strength exceeds 600 MPa while the compressive strength is more than 3000 MPa at the compression rates of 30% under quasi-static conditions. Under dynamic compression conditions, the ultimate compression stresses are 1522 MPa, 1816 MPa, and 1925 MPa with compression strains about 12.8%, 14.7%, and 18.2% at strain rates of 1300 s⁻¹, 1700 s⁻¹ and 2100 s⁻¹, respectively. The dynamic yield strength is approximately linear with strain rate within the specified range and exhibit great sensitivity. The strong localized deformation regions (i.e., adiabatic shear bands (ASBs)) appear in dynamically deformed samples by dynamic recrystallization due to the conflicting processes of strain rate hardening and heat softening. Full article

AlCrFeNi-based high-entropy alloys (HEAs) have emerged as a prominent research system, attracting significant interest due to their compositional diversity and the tunability of their phase structures. However, in practical applications, single-phase AlCrFeNi-based HEAs often face a trade-off between toughness and strength. Therefore, designing multi-phase composite eutectic high-entropy alloys (EHEAs) to optimize their mechanical properties and microstructure has become a key research focus. Si, a common non-metallic element, plays a significant role in strengthening metal materials. In this paper, AlCrFeNi with Si doping strengthening (AlCrFeNi)100-xSix composite EHEAs were successfully fabricated. A systematic analysis was conducted to investigate the impacts of Si doping on the microstructure and mechanical properties of AlCrFeNi-based composite EHEAs. This study shows that with increasing Si content, the biphasic lamellar composite structure at the grain boundaries gradually expands, forming flower petals. The precipitate structure within the grains evolves into flower disks, which form a sunflower-like composite structure in the alloy. The volume fraction of lamellar structures increases in the petals, accompanied by grain refinement. Furthermore, the yield strength of the alloy increases from 1131 MPa to 1360 MPa with increasing Si content. This provides guidance for the design of high-performance composite EHEAs. Full article

Single-phase high entropy alloys (HEAs) exhibit limited mechanical properties while dual-phase and multi-phase HEAs offer better strength, toughness, and stability. In this paper, the as-cast Al_xFe_1.5CoNiC_0.12 HEAs with triple-phase dendritic composite structure is studied, and the influence of the composite structure on the mechanical properties is discussed. The interdendrite (ID) of this structure is composed of a uniformly distributed high-density ordered face-centered cubic structure (L1₂) precipitate phase and face-centered cubic (FCC) matrix, while the dendrite (DR) consists of an ordered body-centered cubic (B2) single-phase. The high density L1₂ precipitate phase leads to a higher hardness in the FCC+L1₂ dual-phase region compared to the B2 single-phase region. The decrease in Al content can greatly improve mechanical performance. The improvement was attributed to the higher volume fraction of the ID and the smaller particle size of the precipitates. The L1₂ phase nano-precipitates exhibit minimal lattice mismatch with the FCC matrix, thereby significantly enhancing the stability of the alloy at the nanoscale. This stability is reflected in the fracture morphology. Modulating the triple-phase dendritic composite structure effectively improves the mechanical properties of the alloy. Full article

This study investigates the effects of nano-oxide dispersoids on microstructural evolution, phase formation, and mechanical properties of W-Mo-Ti alloys reinforced with AlCoCrFeNi_2.1 during mechanical alloying. An EBSD/EDS analysis confirmed the formation of different phases, including the tungsten matrix, FCC reinforcement phase, Al₂O₃, and (Al,Cr) oxide. Y₂O₃ particles played a crucial role in refining the microstructure, promoting a uniform dispersion of the reinforcement phase and oxide particles in the tungsten model alloys. Mechanical testing demonstrates that the Y₂O₃-containing alloy exhibits improved hardness with prolonged milling, attributed to the refinement in the microstructure. In contrast, the Y₂O₃-free alloy shows reduced hardness due to the agglomeration of reinforcement phases surrounded by an (Al,Cr) oxide layer. The model tungsten alloys exhibit brittle behavior in compression tests, which can be attributed to the presence of (Al,Cr) oxide layers weakening the interfacial bonding and limiting plastic deformation. Full article

High-energy structural materials (ESMs) integrate a high energy density with rapid energy release, offering promising applications in advanced technologies. In this study, a novel dual-phase Ti₄₀Zr₄₀W₁₀Mo₁₀ high-entropy alloy (HEA) was synthesized and evaluated as a potential ESM. The alloy exhibited a body-centered cubic (BCC) matrix with Mo-W-rich BCC precipitates of varying sizes, which increased proportionally with the W content. The compressive mechanical properties were assessed across a range of strain rates, revealing that the W10 HEA sustained a compressive strength of 2300 MPa at a strain rate of 3000 s⁻¹. This exceptional performance is attributed to the uniform distribution of circular Mo-W-rich BCC precipitates. Conversely, in the W13 HEA, the aggregated and large Mo-W-rich precipitates deteriorated its dynamic properties. Furthermore, deflagration behavior was observed during dynamic deformation of W10, highlighting its potential as a high-performance ESM. Full article

Today, the machining of heat-resistant alloys based on triple, quad, or penta equilibria high-entropy alloy systems of elements (ternary, quaternary, quinary iron-, titanium-, or nickel-rich alloys), including dual-phase by Gibb’s phase rule, steels of the austenite class, and nickel- and titanium-based alloys, are highly relevant for the airspace and aviation industry, especially for the production of gas turbine engines. Cutting tools in contact with those alloys should withstand intensive mechanical and thermal loads (tense state of 1.38·10⁸–1.54·10⁸ N/m², temperature up to 900–1200 °C). The most spread material for those tools is cutting ceramics based on oxides, nitrides of the transition and post-transition metals, and metalloids. This work considers the wear resistance of the cutting insert of silicon nitride with two unique development coatings — titanium–zirconium nitride coating (Ti,Zr)N and complex quad nitride coating with TiN content up to 70% (Ti,Al,Cr,Si)N with a thickness of 3.8–4.0 µm on which microtextures were produced by the assisted electric discharge machining with the electrode-tool of ø0.25 mm. The microtextures were three parallel microgrooves of R0.13^+0.02 mm at a depth of 0.025₋₀.₀₅. The operational life was increased by ~1.33 when the failure criterion in turning nickel alloy was 0.4 mm. Full article

Previous studies have focused on the laser cladding of high-entropy alloys (HEAs) on untreated H13 steel, yielding promising results. However, there is limited research on laser cladding HEAs on heat-treated H13 steel, which is more common in the automotive mold industry. In this study, CoCrFeNiAl/WC high-entropy alloy composite coatings were fabricated on heat-treated H13 steel using laser cladding, addressing the gap in applying HEAs on heat-treated tool steels. The influence of the WC content on the phase composition, microstructure, and mechanical properties of the composite coating was investigated. The coating exhibits a dual-layer microstructure consisting of a working layer and a transition layer with different compositions. The results indicate that the CoCrFeNiAl/WC working layer primarily consists of FCC phases. As the WC content increases, metallurgical reactions occur in the working layer, forming (Fe,Co)₃W₃C, Co₄W₂C, and Cr₇C₃ carbide precipitates. This significantly enhances the hardness and wear resistance of the coating, with the final hardness being 1.23 times that of the substrate, the wear weight loss being only 0.21 times that of the substrate, and the average friction coefficient being only 0.82 times that of the substrate. Full article